Overweight and obesity in children and adolescents is a significant global health concern, although rates appear to have plateaued in some developed nations, including Australia. However, inequalities persist, with higher prevalence among culturally and linguistically diverse (CALD) groups, Aboriginal and Torres Strait Islander peoples, and socioeconomically disadvantaged families. This study aims to identify specific cultural and ethnic groups at higher risk of overweight and obesity during childhood and adolescence, acknowledging the complex interplay between cultural, socioeconomic, and environmental factors influencing adiposity. Australia's increasing cultural diversity due to high immigration rates necessitates understanding how these factors influence children's weight across developmental stages. Previous cross-sectional studies have revealed higher odds of overweight and obesity in some priority populations, particularly immigrants from low-and-middle-income countries and Aboriginal and Torres Strait Islander children. The "double disadvantage" of ethnicity and low SEP has also been noted. However, no prior research has examined the longitudinal relationship between priority populations and zBMI from early childhood to late adolescence, identifying critical developmental periods during which zBMI differences emerge. Addressing this knowledge gap is crucial for developing culturally relevant and accessible interventions to reduce health inequalities.

Existing literature highlights the disparities in childhood overweight and obesity across various population groups. Studies show higher prevalence among CALD communities, Aboriginal and Torres Strait Islander children, and those from lower socioeconomic backgrounds. A "double disadvantage" effect, where the combined impact of ethnicity and low socioeconomic status exacerbates obesity risk, has been observed. While cross-sectional studies have identified associations between specific ethnicities and weight status, longitudinal studies examining these relationships across diverse age groups are limited. The literature also emphasizes the complex interplay of factors—cultural norms, lifestyle behaviors, dietary shifts, acculturation, and access to healthcare—that influence weight development in children from different backgrounds. The lack of longitudinal data covering the entire childhood and adolescent period hampers the development of effective, targeted interventions. This research aims to address these gaps by employing a robust longitudinal design.

This study utilized data from the Longitudinal Study of Australian Children (LSAC), encompassing the "baby" (B) and "kindergarten" (K) cohorts. Data from waves 2-8 were analyzed, representing 9417 children aged 2-19 years and over 100,000 person-years of follow-up. Children were classified into nine cultural and ethnic groups based on parental and child's country of birth and language spoken at home, including a specific Aboriginal and Torres Strait Islander group. Socioeconomic position (SEP) was determined using a composite score based on parental education, occupation, and family income, categorized into quintiles. The primary outcome measure was zBMI, calculated using age- and sex-adjusted WHO growth standards. Multilevel mixed linear regression models were used to analyze the association between cultural/ethnic group and SEP with zBMI, stratified by three developmental periods: early childhood (2-5 years), middle childhood (6-11 years), and adolescence (12-19 years). For cultural/ethnic group analysis, an unadjusted model was used; for SEP analysis, adjustments were made for cultural/ethnic group. Survey weights were not applied due to cohort pooling. Missing data were minimal and imputation was not deemed necessary. Ethical approvals were obtained from relevant ethics committees.

The study revealed significant differences in zBMI across cultural and ethnic groups and SEP levels throughout childhood and adolescence. Compared to the English-speaking reference group, children from the Middle East and North Africa, Americas, and Oceania consistently showed higher zBMI across all three developmental periods. In contrast, children from South and Central Asia and Sub-Saharan Africa exhibited lower zBMI. Aboriginal and Torres Strait Islander children had lower zBMI in early childhood but higher zBMI in middle childhood and adolescence. A consistent socioeconomic gradient was observed, with higher zBMI strongly associated with greater socioeconomic disadvantage across all age groups. Specific findings regarding the magnitude of zBMI differences for each group across the three developmental periods are detailed in the paper (see Figures 1 & 2 and supplementary tables).

The findings highlight that weight development in Australian children is culturally patterned and influenced by socioeconomic factors. The consistent association of higher zBMI with socioeconomic disadvantage emphasizes the need to address health inequalities. Identifying specific cultural and ethnic groups at higher risk at different ages provides crucial information for developing targeted interventions. For example, early childhood programs may not be as suitable for Aboriginal and Torres Strait Islander children who show lower zBMI initially. Conversely, programs targeting early childhood (ages 2-5) could be beneficial for those from the Middle East and North Africa, the Americas, and Oceania. Middle and high school programs would be relevant for Aboriginal and Torres Strait Islander children, as well as those from the Americas, the Middle East and North Africa, and Oceania. The results support the effectiveness of culturally tailored obesity prevention programs, advocating for more such initiatives in Australia, particularly given the current lack of programs specifically addressing Aboriginal childhood obesity. Policymakers can utilize these findings to develop strengths-based, community-led approaches and adapt existing programs to better serve these key populations.

This study provides compelling evidence that the prevalence of overweight and obesity is culturally patterned in Australian children, with significant disparities among priority populations. Understanding these population-specific risks across different age groups allows for targeted resource allocation and the development of culturally tailored healthy weight programs. Future research should focus on developing and evaluating culturally adapted interventions across various developmental stages and exploring the underlying mechanisms driving these disparities.

The study's limitations include the use of proxy measures for cultural and ethnic group classification, potentially leading to some misclassification. The small sample sizes for some groups prevented further subgroup analysis and sex-stratified analysis. Additionally, the analysis did not utilize survey weights, potentially affecting the generalizability of findings to the entire Australian child and adolescent population. Despite these limitations, the large sample size and longitudinal design strengthen the study's overall contribution.